Currently, power generation from an external or internal heat source using thermal energy conversion technologies such as solid-state thermionics and thermoelectrics or dynamic conversion with Otto, Stirling, Brayton, or Rankine technologies are fundamentally limited in their maximum specific power due to either their low efficiency and/or operating frequency. The solid-state technologies are low voltage and hence produce a high DC current which restricts their minimum geometry to approximately 4 A/mm2 to avoid over-heating. Hence, high power implementations of this technology class are inefficient, large, and heavy.
In addition, the dynamic technologies are limited to approximately 400 Hz because of two different reasons. First, the oscillating piston engines such as Stirling and Otto technologies require a force on the piston that grows exponentially with frequency, which is difficult to achieve above 400 Hz with reactive springs or rods. Second, the rotating machines such as Brayton are also limited in frequency of operation because above 24,000 RPM (400 Hz) the rotor tip speed either becomes supersonic or places too much stress on the rotor due to centrifugal forces. Hence, today's space, terrestrial, and proposed aircraft power systems are unnecessarily large and heavy for the power level they provide.